Detect Keyboard Input Matlab

Question

I have a simple question, although it's harder than it seems; I couldn't find the answer on the interwebs :O

I'm writing a script in Matlab. What I want to do is the following:

• When I press the esc key, I want a helpdialogue to pop up, so my script pauses. (So when I press esc, I want to stop the whole script to run so that the car (which im writing the script for) stops driving)

How do I do this? How can I say to Matlab: When I press esc, do this...

Thanks for your time guys!

EDIT: It's no option to implement something which awaits the keypress. Im writing a script for a driving car. It just has to drive around basically, but when I press esc for example, it should stop driving. So the script just has to run, untill I press the esc key; then the script has to pause.

Answer 1

In a matlab figure you can define a 'KeyPressFcn' that works similar to do what you ask.

If you are in the console you have to work around that matlab is single threaded. Basically you need to halt the program flow to check for key presses.

btw - also when you use 'KeyPressFcn' you will need to make some pauses so that Matlab will check if anything has happened.

btw2 - I should also add during this pauses Matlab will not only read your key presses - but also do some housekeeping such as redrawing its window and stuff.

Answer 2

KeyPressFcn is good because it forces you to write event-driven code. Which is generally a good idea! However, if KeyPressFcn doesn't seem right for you, for example if you must keep running in a loop, and you just want to poll whether a key has been pressed, I found this solution buried in the matlab website:

get(gcf,'CurrentCharacter')

Then you could set this property to a blank, and poll it as required. e.g:

finish=false;
set(gcf,'CurrentCharacter','@'); % set to a dummy character
while ~finish
  % do things in loop...

  % check for keys
  k=get(gcf,'CurrentCharacter');
  if k~='@' % has it changed from the dummy character?
    set(gcf,'CurrentCharacter','@'); % reset the character
    % now process the key as required
    if k=='q', finish=true; end
  end
end

This worked well for me in 2014b. The downside is that the graphics window needs to be focused to receive the key events.

Answer 3

I frequently ran into similar use cases and typically preferred to react to joystick buttons because of the more convenient interface provided by vrjoystick. However, I recently wrote a library that provides a similar interface for keyboard inputs.

% Pause on ESC
kb = HebiKeyboard();
while true
    state = read(kb);
    if state.ESC
      % PAUSE DRIVING
    else
      % DRIVE CAR
    end
end

It's non-blocking and doesn't require focus on any particular figure.

File Exchange: http://mathworks.com/matlabcentral/fileexchange/61306-hebirobotics-matlabinput

Github: https://github.com/HebiRobotics/MatlabInput

Answer 4

I had a related task once, and i did it with getkey form matlab file exchange. Basicly you will want to have it listen for ascii 1B (27 decimal)

if getkey does not solve your problem you can still have a look at its code and maybe find the line that will do the trick for you.